290 



THE INDIA RUBBER WORLD 



{Febri 



1920. 



of cure to increase again, the average decrease is only 16 per 

 cent ; keeping in water for 48 hours gives a still smaller decrease, 

 on the average 11.7 per cent. The maturation gradually tends 

 to equalize the effect of the extraction of serum substances, and 

 freshly rolled sheet kept seven days under vi'ater shows a time 

 of cure of 55 minutes, nearly that of matured rubber. 



(5.) Soaking sheet rublicr in water docs iiol prevent rusti- 

 ness. 



(6.) Keeping the freshly rolled sbeels in water for some 

 time is of prime importance, not only to prevent the cases of 

 greasiness (.hydroscopic serum substances on the surface ot 

 ihe sheet), but to diminish the tendency to moldiness. 



(7) Keeping the unrolled coagulum in water gives similar 

 results, but the efTecl differs w^ith the thickness and hardness 

 of the coagulum. 



The simplest way to prevent rustiness in actual estate prac- 

 tice is to take care that the surface of the sheet dries so rapidly 

 that the micro-organisms, that grow only on the surface ex- 

 posed to the air and need moist surroundings, have no time 

 to develop. 



CONCLUSION. 



The defect called "rustiness" in sheet rubber is not caused 

 by a film of serum-substances, notably proteins, dried on the 

 surface of the sheet, but it is formed by decomposition of the 

 serum-substances by an jerobic micro-organism. 



THE CAUSE OF RUSTINESS IN SHEET RUBBER. 



In the Communications of the Central Rubber Station,' H. J. 

 Hellendoorn discusses the causes of rustiness in sheet rubber, 

 summarizing his experiments as follows : 



In experiments in the laboratory and on estates, rustiness 

 was always produced at will by keeping the freshly rolled 

 sheets for some time, 24 or 48 hours, in a moist atmosphere. 

 The degree of moisture of the atmosphere in which the sheet 

 hangs shortly after rolling, is of the greatest importance. Sheets 

 taken immediately after rolling into a drying room of higher 

 temperature (40 to 60 degrees C.) never show rustiness, while 

 air drying at room temperature produces rustiness during 

 periods of wet weather. 



When coagulum is kept in the dishes some time after coagu- 

 lation, as over night, the side of the sheet that corresponds 

 to the upper part of the coagulum — the layer that was exposed 

 to the air, shows rustiness to a larger extent than the lower 

 parts of the coagulum. The explanation is that on the surface 

 of the coagulum the infection, and perhaps a growth of the 

 perobic micro-organisms may start earlier. 



Rustiness can be prevented by disinfecting the surface of 

 the freshly rolled sheet by soaking it for some time in dilute 

 solutions of formalin, chinosol, or bisulphite. The same dis- 

 infecting effect may be produced by keeping the freshly roiled 

 sheet for some time in the vapors of boiling water, or by 

 immersing the sheets in hot water (60 degrees C.) This is 

 the well known method formerly used to prevent rustiness and 

 surface oxidation by enzymes. 



The micro-organisms causing rustiness are aerobic ; that is. 

 they need air for their growth and do not thrive where the air 

 cannot penetrate. For instance, when a freshly rolled sheet is 

 tightly rolled up and placed in a moist atmosphere, only the 

 parts exposed to the air develop rustiness, while the parts of 

 the surface that stick together, so that the air cannot penetrate, 

 remain free of rustiness. Like all micro-organisms, those caus- 

 ing rustiness have an optimum temperature (about 40 degrees 

 C). 



The thin layer of serum-substances that remains on the sheet 

 after most of the serum has dripped off, or the by-substances 



"Archiej 



Rubber Cii 



October, 1919. page 431 



absorbed by the rubber, form the sources of nourishment for 

 the micro-organisms. Dilute serum seems to be preferred to 

 the undilute. Soaking the sheets in water after rolling, so 

 that a great part of the soluble serum-substances is removed, 

 does not prevent rustiness. In fact, under favorable circum- 

 stances rustiness develops on such sheets to a much larger 

 degree. It is well known to planters that when sheets are 

 soaked in water and the dilute serum so formed is kept for 

 some time, a jelly-like substance develops, as if some grease 

 or fat had been extracted from the sheets. This jelly-like 

 substance is probably closely related to the substance forming 

 the film of rustiness. 



The question is of some practical importance whether smoke 

 forms a sufficient disinfectant to prevent the growth of the 

 organisms causing rustiness. Wet sheets hung in a smoke 

 house at a somewhat elevated temperature and without much 

 ventilation would be under favorable conditions for the develop- 

 ment of micro-organisms, unless the smoke acted as a pre- 

 ventive. It seems that smoke does hinder the formation of 

 rustiness under such circumstances to some extent, but does 

 not wholly prevent it ; and especially in places where the smoke 

 does not penetrate so easily, for instance, near the sticks, or 

 in places where two sheets come very close together, rustiness- 

 may develop. If care is taken that the sheets air-dry rapidly, 

 so that they are sufficiently dry when they are placed in the- 

 smoke house, the disinfection by smoke is of no further im- 

 portance. 



DETERMINATION OF IRON AND ALUMINUM. 

 By C. B. Clarke. 



The following is a method for the quantitative determination 

 of iron and aluminum in ignited mixtures containing much greater 

 amounts of alumina than ferric oxide. 



The finely divided oxides are intimately mixed with acid potas- 

 sium fluoride in a platinum crucible. The mixture is fused over a 

 small flame until, after a few minutes, it becomes solid. Dilute 

 sulphuric acid is then added, and the greater part of the hydro- 

 fluoric acid expelled by heating for a short time. The sulphates 

 are then dissolved in water in a platinum dish ; the iron is re- 

 duced by sulphur dioxide, the excess of which is expeJled by 

 carbon dioxide, the liquid is then titrated with permanganate of 

 potassium in a Jena glass beaker. 



In one analysis by this method, in which 0.007-gram FcjOj was 

 present in 0.094-gram of mixed oxides, 0.0065-gram Fe^Os was 

 found. 



The presence of considerable quantities of potassium hydrogen 

 fluoride does not interfere with the titration. 



The advantages of this method over that of fusing with potas- 

 sium bisulphate are that no platinum passes into solution, and 

 that it is much quicker. 



INFERIOR GRADES OF RUBBER. 



Dr. A. J. Ulte' has investigated the inferior grades of rubber 

 to determine whether, besides the differences in external appear- 

 ances, the internal qualities of such kinds of rubber show any 

 difference. For this purpose the viscosity and the percentage 

 of ash were ascertained from samples of pale and dark scrap 

 of the same estate. The dark scrap gave a lower viscosity fig- 

 ure (averaging 97 against 113 for pale scrap) and a higher ash 

 per cent (averaging 0.68 against 0.51 for pale scrap). 



M.\XIMILI..\N TOCH, OF TOCH BROTHERS, MAKERS OF CHEMICALS 



and technical paints, has been appointed Adjunct Professor of 

 Applied Chemistry at Cooper Institute, New York City, where 

 he will give a course on the chemistry of india rubber. 



* Commun 



